SND SC6820 Plaform Maintain Guide

Version: 1.0.0

Date: 2012-10-15

Chapter 1. Mobile theory instruction

一.1 Hardware Instruction

SC6820 reference platform hardware circuit comprising: baseband chip, the radio frequency section, the

memory section, the display part, audio part, power source part, the peripheral device (Wifi, BT, the GPS),

etc.. For details, refer to Figure 1-1 shows the SC6820 platform reference hardware overall block diagram of

the mobile phone.

1

Hardware overall block diagram of Figure 1 1 SC6820

一.1.1 Major components introduction

一、BB chip introduction

二、SC6820 GSM/GPRS/EDGE Multimedia baseband chip for developers to design high-performance GSM / GPRS /

EDGE Android smartphone to provide a cost-effective solution. Integrating rich multimedia capabilities in the

new generation of smart phones, and its peripheral circuit design is simple and flexible according to customer

demand for a variety of functions and applications currently popular.

三、RF chip introduction

SR1018 Is a support for quad-band GSM / GPRS / EDGE terminal RF transceiver, which uses CMOS

technology, an area of 4 × 5 mm2, it can be convenient with Spreadtrum's SC6820 Baseband chip can be

used with a variety of power amplifier (PA) and the antenna switch.

key signal requirements

26M clock signal

Figure 1 1 BB 26 M the clock MCLKI clock requirements

Form 1 1 BB 26 M clock parameters

32K clock signal

32K clock requirement：32.768K;+/-20ppm;12.5pf/9pf

Sensor clock singal

Sensor The clock requires reference to the following figure, note the parameters.

图 1-1 Sensor 输入时钟 图 1-2 Sensor 输出时钟

SIM card signal

一． The order of the SIM card：1. RST 2. VCC 3. I/O 4.CLK

二． SIM Voltage requirements: 3V+/-10%

三． SIM CLK Signal requirements: high level between 3.15 and VCC +0.3 V low minimum

between -0.3 ~ 0.7V; rise time is not more than 50ns clock cycle and not more than 9%; duty

cycle at 40~ 60%; clock frequency 3.25M.

四． SIM IO Signal requirements: a high level between 3.8 and VCC +0.3 V low minimum -

0.3 ~ 0.4V of; rise time is less than 1us; fall time, tens of ns.

T Card Signal

Figure 1 4 T card write operation timing

Figure 1 5 T card read operation timing

Audio signals

一．Handset, Speaker, headphone no obvious 217Hz RF noise, compare the picture below

Figure 16 217Hz noise 17 no obvious 217Hz noise

一．Headset, Speaker no obvious murmur.

一.2 Software Download

一.2.1 Download workflow

SC6820 chip power boot from ROM, after first detection U1TXD/NBOOT, state judge NBOOT pin, if U1TXD for low

into USB download mode; If U1TXD high, and then detect the button, USB download mode specific the keys

(KEYIN0 KEYOUT0 combination) press enter; if there is no specific button is pressed, the UART0 and UART1

polling receive, if any of 80ms withina UART port (UART0 and UART1) received from the download tool 3 0x7E into

the UART download mode, 80ms within two UART port (UART0 and UART1) did not receive 3 0X 7E, enter the

NAND BOOT modenormal boot. Detailedprocess, you can referto Figure

Figure 1 9 SC6820 BOOT way

一.2.2 The 1.2.2 boot process description

1、 Spreadtrum Android platform boot interrupt two kinds:

2、 The boot key press PBINT low (ground), boot interrupt.

3、 The charger into the generate Charge interrupt.

4、 alarm interrupt.

In addition, Spreadtrum platform, the power-on self-test function, the phone automatically boot

mode is turned on automatically boot on power. Auto-boot mode can be modified by modifying

the of NV parameters or phone to enter the engineering mode.

Attention：

The Spreadtrum SC6820 platforms have the power-on self-test function, so normal phone,

power-on, the phone will be about 120mA current, when the self-test end, shut down! The current

restored to the shutdown current.

一.3 Power Management

SC6820 integrates two DCDC, 25 adjustable LDO, the power demand to meet the the SC6820 chip internal and external devices, which greatly reduces the cost of a mobile phone peripheral. Power input and power output of each interface separation, increase the flexibility of the external power supply selection and device selection, and convenient power consumption debug.

一.3.1 internal LDO description

SC6820 power management is shown in Figure 1-10. The SC6820 chip built PMU functions, baseband

chip and peripheral circuits provide power management supply SC6820 phone can choose to configure an external

DC / DC power supply device.

图 1-10 SC6820 内部 LDO 示意图

一.3.2 Charge Management

SC6820 platform support charger and USB charging two charging, the charging process, the pre-charge, constant

current charge, constant voltage charge in three stages.

一.4 Clock Design

一.4.1 Real-time clock design

图 1-11 RTC 时钟电路

一.4.2 System Clock Description

SC6820

MCLKI GPI2

WIFI/BT

CLK_REQUEST

XTAL_IN

SR1018GPS

CLK_IN

图 1-12 26M 时钟框图

Chapter 2. Maintain Guide

一.5 can not download

The download process, you can refer to the instructions of the previous chapters.

Can not download most of the problems arise because the IO interface on the PCB or the BB chip Weld even welding

caused, carefully check the PCB welding is a very important step. Exclude welding problems, if the problem persists,

step-by-step analysis of the circuit. Detailed reference to the following flowchart.

Figure 21 can not download the repair process

一.6 Can not power on

The handset open process can be found in the previous chapter。Can not power on mostly cause by PCB fake weld ,even weld,it will lead to chipset out of work .If power supply correctly still can not open phone,it must by 26M or 32.768K clock out of working

Referring specifically to the following process chart。

Chart 2-2 can not working repair processes

Figure 2 3:32 K failure analysis process

Figure 2-4 26 M failure analysis process

一.7 Power Failed supply

Power failed supply mostly cause by IO port connect not good, normally is PCBA have IO port fake weld or even weld.\

Charging cable connector pin loose also can lead to connect not good, try to change cable.

。Referring specifically to the following process chart。

Figure 2-5: Charging schematic (SC6820 same）

Chart 2-6 will not charge maintenance processes

一.8 LCD displayed not correctl

LCD displayed not correctly because EMI filter Fake Weld, even welding；or LCD module FPC destroy, connect port destroy，。Please refer to the repair process

Figure 2- 7 LCD reference circuit diagram (SC6820 data line 24, rarely use resistance TP）

Chart 2 -8 LCD display abnormal repair process

一.9 Touch panel not working

SC6820 chipset use capacitance touch panel,by exterior touch panel control IC ,control panel inspection function.Touch panel not working cause by assembly not good,TP destroy,TP port not working or touch control IC welding not good

Specific overhaul process see chart 2-9；

　Capacitive touch screen control schematic

Figure 29 touch screen repair processes

一.10 LCD backlight not light

Smart handset disply require high brightness,in order to improve backlight brightness need use 8---12 LED or more LED lens, meanwhile to keep all lens brightness the same need use Series backlight circuit, Basic principles as shown below, specific repair processes see chart 2-10

LCD backlight driver circuit

Chart 2-10 backlight not light repair process chart

一.11 SIM card not identify

Not identify SIM card mostly cause by card seat weld not good or destroyed,sometime might by the Shunt capacitance of the signal line even tin, Short circuit etc. Specific maintenance processes reference chart 2-12；

Chart 2 -11 Sim card circuit (SC6820 principle is the same）

Chart 2 -12 SIM card repair process

一.12 T- Flash not identify

T card not identify mostly cause by T card seat welding not good or flip touch not closely；

Figure 2 -13 T -card circuit

Figure 2-14 T-card repair process

Camera not workingCamera not working

一.13 Camera not working

Camera not working mostly cause by touch not good,e.g.. insert not correctly,insert not fastness,the

port weld not good. Specific maintenance processes reference chart。

　Figure 2 15 Camera circuit diagram

Chart 2 16 Camera abnormal repair process (Figure Sensor which represents the Camera）

一.14 Side key invalidation

SC6820 support 8×8 keyboard matrix ， but smart handset side key more less,so power switch

special treatment,one side connect PBINT PIN OF SC6820，another side grounding.the key most use

FPC weld way,so key invalidation most cause by FPC destroy or weld not good, but sometime by BB

welding not good or PCB problem.

Chart 218 keyboard failure repair process

一.15 MIC silence

MIC selence normal by MIC destroy or MIC access parts fake weld,even weld or weld not good then parts destroy.If the volume lower than normal ,it cause by MIC polarity weld on contrary side.our model most MIC

are in the sub-PCBA connect with the motherboard circuit connection by FPC,so touch not fastness can lead to silence.

Specific maintenance process parameters see The test chart is 2-20；

Chart 2 19 Mic schematics

Chart 2 20 Mic to uplink silent maintenance process

一.16 Receiver silence

chart 2-21 receiver circuit diagram

Chart 2-22 receiver silence repair process

一.17 Speaker silence

Chart 2-23 Speaker circuit diagram

Chart 2 -24 Speaker silent repair process

一.18 Earphone abnormity

Earphone can not identify and silence, mostly cause by earphone port connect not good or the relative part welding not

good. A few is cause by relative circuit part destroy,or BB chipset welding not good.

Specific maintenance processes reference chart 2-26；

chart 2-25 earphone circuit diagram

Chart 2-26 headphones silent maintenance process

一.19 Vibrator not working

马达 Vibrator not shaking normal cause by vibrator destroy, the vibrator control line directly connect with BB chipset.

If get rid of by welding, try update software ensure still not working,try remove welding again to change BB chipset.

一.20 Flash len not shining

Flash len most use FPC welding with PCBA, the len not shine most cause by FPC destroy or weld not good.

If not, it might by relative parts weld not good or destroy,

The specific repair process reference chart to 2-28；

Chart 2-27 camera flash drive circuit

Chart 2-28 flash light maintenance processes

一.21 The ambient light sensor is invalid

Our model light sensor use FPC connect with PCBA,light sensor invalid need check the seal

around

Chipset whether good enough not to light leakage.

If not,it might be FPC destroy or connect not good.

Specific maintenance processes reference chart 2-29；

Chart 2-29 light sensor invalid maintenance processes

一.22 Signal weakness, WLAN invalid

The handset signal weakness,WLAN invalid most cause by the port problem which antenna

connect with PCBA,RF line port loose,some metal parts grounding problem.

Calibration the PCBA comprehensive measurement to inspect the Conduction properties whether OK, If OK,

focuson check the port of connect PCBA with RF line. Whether welding not good or destroy

The specific maintenence processes reference chart 2-30

Chart 2-30 signal, network maintenance process

一.23 the peripheral equipment problem

SC6820 have lots of peripheral ports to add various function device.e.g. Wifi、BT、GPS、ATV、FM

etc.

To repair these device,usually be divided into two categories:

1 .the device failed start,usually cause by the device chip or peripheral parts weld not good.

After get rid of weld problem, Refer to the following chart 2-31 for maintenance；

Chart 2-31 peripherals can not open

2. the performence badness e.g. Wifi speed too slow or can not connect,BT distance short,GPS not

locate,ATV

And FM search problem, it most by relative antenna connect not good,RF access weld not good or

destroy.

Specific maintenance methods refer to chart 2-32

Chart 2-32 peripherals short distance, poor performance maintenance process

一.24 RF maintenance problem guide

When usual use handset have not signal and dial problem, should try PCBA calibration

comprehensive measurement first to ensure RF performance indicators whether OK.

In that course it mitht appear AFC、APC、AGC not good will lead to testing fail situation ,as following

Separate to introduce maintenance method:：

一.24.1 AFC Fail

Adverse Reference Chart 2-33 steps for maintenance, such as replacing the devices still can use the shows

calibration AFC FailOscilloscope, spectrum analyzers and other instruments combined with Mobile Tester tool to

measure the RF control signal and the node RF signal accurately locate further maintenance;

图表 2-33 AFC Fail 维修参考

一.24.2 APC Fail

Adverse Reference Chart 2-34 steps for maintenance, such as replacing the devices still can use the shows

calibration APC Fail

Oscilloscope, spectrum analyzers and other instruments combined with Mobile Tester tool to measure the RF

control signal and the node RF signal accurately locate further maintenance;

图表 2-34 APC Fail

一.24.3 AGC Fail

Overwhelming majority of adverse receiver AGC Fail reasons pathway components poor welding lead, need to

focus on examination of SAW and its matching circuit, the specific 维 修 步 骤 可 参 考 图 表 2-35 ；

图表 2-35 AGC　Fail 维修步骤

一.24.4 MobileTester tool instruction

MobileTester tool is a common platform Spreadtrum its function is very powerful debugging tools, this is

mainly a brief description of the RF in the repair process can

Use this tool to quickly determine the positioning of the tool allows non-signaling mode phone is in force

transmitting and receiving our by state

Current and output power when the phone information to locate the problem.

The AFC repair, MobileTester reference set as follows:1. 打开 MobileTester 工具 ;

1. Serial port settings and select CAL MODE, test status to enter the mobile phone powerClick on the "Active". Click "Set Band" select EGSM900 band3. Set: the Channel 61, PCL: 5, the CDAC value is set to 55, CAFC is set to 7000, the point of the TX ON;4. Read instrument frequency error5. Adjust the the CDAC values (45-63), keep CAFC value unchanged, Frequence Error absolute value less than 450HZKeep CDAC constant adjustment CAFC value measurement frequency error, calculate the frequency error with the CAFC value changes in the slope of the CAFC the slope of between 4-10 Hz / bit, the AFC calibration Pass Note: CDAC and CAFC value adjustment should be first off the transmitter to set

The APC maintenance, MobileTester reference set as follows:1 open MobileTester tools;

Serial port settings and select CAL MODE, test status to enter the mobile phone powerClick on the "Active". Choose to test the band EGSM / DCS Click "Set Band"Setting: Channel 61/698, Pcl: 5/0 Power Factor value is set to 32767;Read instrument power

Chapter 2 Maintain Skill

Any repair, the first step to use a multimeter measurement Vbat Vchg on to whether there is a short circuit. Avoid greater damage on power.Overhaul circuit, based on simple to complex, from the majority of cases to the principle of the few cases, such as the current situation, you should begin to start the external interface and external LDO last doubts BB chip replacement of the BB chip is the most tedious; still large current the probability of the situation, BB chip power input pin is shorted to ground is greater than the the RF PA chip power shorted probability, so maintenance is necessary to first analyze the BB chip troubleshoot RF PA chip. And so on other problems.

Patch parts, such as Camera, LCD, Speaker, Vibrator, Mic, etc., if the visual interface or circuit Weld, and even

welding phenomenon, tested replacement parts can easily be identified.

Not able to solve the problem of maintenance in accordance with conventional methods to measure the voltage or

waveform to accurately locate the problem, instead of blindly replacement devices, otherwise easily lead to

confusion maintenance.